It is known to use naturally occurring extracelluar matrices (ECMs) to provide a scaffold for tissue repair and regeneration. One such ECM is small intestine submucosa (SIS). SIS has been described as a natural biomaterial used to repair, support, and stabilize a wide variety of anatomical defects and traumatic injuries. The SIS material is derived from porcine small intestinal submucosa that models the qualities of its host when implanted in human soft tissues. Further, it is taught that the SIS material provides a natural matrix with a three-dimensional structure and biochemical composition that attracts host cells and supports tissue remodeling. SIS products, such as OASIS™ and SURGISIS™, are commercially available from Cook Biotech Inc., Bloomington, Ind.
Another SIS product, RESTORE® Orthobiologic Implant, is available from DePuy Orthopaedics, Inc. in Warsaw, Ind. The DePuy product is described for use during rotator cuff surgery, and is provided as a resorbable framework that allows the rotator cuff tendon to regenerate. The RESTORE Implant is derived from porcine small intestine submucosa, a naturally occurring ECM composed primarily of collagenous proteins, that has been cleaned, disinfected, and sterilized. Other biological molecules, such as growth factors, glycosaminoglycans, etc., have also been identified in SIS. See: Hodde et al., Tissue Eng., 2(3): 209 217 (1996); Voytik-Harbin et al., J. Cell. Biochem., 67: 478 491 (1997); McPherson and Badylak, Tissue Eng., 4(1): 75 83 (1998); Hodde et al., Endothelium 8(1): 11 24; Hodde and Hiles, Wounds, 13(5): 195 201 (2001); Hurst and Bonner, J. Biomater. Sci. Polym. Ed., 12(11): 1267 1279 (2001); Hodde et al., Biomaterial, 23(8): 1841 1848 (2002); and Hodde, Tissue Eng., 8(2): 295 308 (2002). During seven years of preclinical testing in animals, there were no incidences of infection transmission from the implant to the host, and the SIS material has not adversely affected the systemic activity of the immune system. See: Allman et al., Transplant, 17(11): 1631 1640 (2001); Allman et al., Tissue Eng., 8(1):53 62 (2002).
While small intestine submucosa is available, other sources of ECM are known to be effective for tissue remodeling. These sources include, but are not limited to, stomach, bladder, alimentary, respiratory, and genital submucosa. In addition, liver basement membrane is known to be effective for tissue remodeling. See, e.g., U.S. Pat. Nos. 6,379,710, 6,171,344, 6,099,567, and 5,554,389, hereby incorporated by reference. Further, while ECM is most often porcine derived, it is known that these various ECM materials can be derived from non-porcine sources, including bovine and ovine sources. Additionally, the ECM material may also include partial layers of laminar muscularis mucosa, muscularis mucosa, lamina propria, stratum compactum layer and/or other such tissue materials depending upon other factors such as the source from which the ECM material was derived and the delamination procedure.
The following patents, hereby incorporated by reference, disclose the use of ECMs for the regeneration and repair of various tissues: U.S. Pat. Nos. 6,379,710; 6,187,039; 6,176,880; 6,126,686; 6,099,567; 6,096,347; 5,997,575; 5,993,844; 5,968,096; 5,955,110; 5,922,028; 5,885,619; 5,788,625; 5,733,337; 5,762,966; 5,755,791; 5,753,267; 5,711,969; 5,645,860; 5,641,518; 5,554,389; 5,516,533; 5,460,962; 5,445,833; 5,372,821; 5,352,463; 5,281,422; and 5,275,826.
Tissue engineering attempts to replace diseased tissues of the body with engineered replacements. One of the most important applications of tissue engineering is for treatment of cardiovascular diseases. Clinical treatment of disease and trauma to the coronary arteries and the peripheral vessels often includes the use of bypass grafting. In 2006, approximately 448,000 cardiac revascularizations were performed in the United States alone.
The choice of the graft is critically important and plays a major role in the success of the procedure. Autologous grafts are most often used, and are typically taken from the saphenous vein, internal mammary artery, or the radial artery2. This method, however, is not always an option since many patients do not have a vein that is suitable to use. Also, the costs associated with harvesting autologous vessels are considerable, and there is a significant level of morbidity associated with the procedure3.
Synthetic grafts such as Dacron or polytetrafluoroethylene have also been used with some success. When it comes to the treatment of small diameter vessels, however, the use of these grafts tends to lead to poor compliance and low patency, often resulting in thrombogenicity due to lack of endothelial cells and anatomic intimal hyperplasia4. Thus, an alternative graft is sought that can meet the disadvantages and shortcomings seen in both autologous and synthetic grafts.
Recently, tissue engineering has been looked at as a promising solution to the issues at hand. Such methods often include developing a scaffold that is seeded with cells in vitro or implanted and allowed to repopulate in vivo. By decellularizing either xenographic or human based tissue and repopulating it with the recipient's own cells, a scaffold can be derived that, in theory, eliminates the need for immune-suppressant drugs and reduces the risk of graft rejection. Such a scaffold consists of an extracellular matrix (ECM) that is not only rich in cell signaling components essential for cell adhesion, migration, proliferation, and differentiation, but also has a greater resistance to infection than synthetic materials5.
Recent research has focused on a variety of tissue decellularization methods. Many different protocols have been tested that typically include some combination of physical, chemical, and/or enzymatic processes3,6,7,8. Though the results from such work have shown promise, there has been little long term follow-up2. These methods also risk damage to the ECM, possibly compromising the scaffold's further development and integration into the recipient's body9. For example, chemicals used in the treatment process may not be completely removed after use. These chemicals could prove toxic to the host cells9 and result in long term stenosis in vivo due to insufficient cell ingrowth7. Also, some chemical treatments used such as acids, non-ionic detergents, and ionic detergents may remove important molecules such as GAGs from collagenous tissues, resulting in slowed cell migration and a reduced chance for the tissue to properly remodel in vivo9. Enzymes used to decellularize the tissue such as DNase, RNase, and trypsin could also pose a problem, invoking an adverse immune response by the host9. Physical techniques are also not without potential risk, and methods such as snap freezing and mechanical agitation can disrupt the ECM as the cellular material is removed9. Some of these issues, such as insufficient cell ingrowth in vivo, can be addressed by seeding the scaffolds in vitro prior to implantation. These techniques, however, require time (typically at least 8 weeks), local expertise, and bioreactor facilities5, making them both costly and impractical for emergency procedures.